Reams (i.e., 500 sheets) of cut paper (8½×11, etc.) for copy machines, computers, printers, and other applications are most commonly packaged for shipping, storage, and retail sale in ream wrappers made of various wrap materials. These wrap materials traditionally have been paper (poly coated or two papers laminated with poly), plastic film, or a paper/solid plastic film combination. In addition to encasing reams of paper, the wrap materials protect the wrapped paper product from physical damage and moisture pickup during shipping and storage. The wrap materials also protect the wrapped product from physical damage during repeated handling and stocking on retail shelves.
As small offices and home offices have proliferated, the distribution of reams of paper has changed from boxes for large users to wrapped reams for retail stores and the small office and home office segments. Retail and in-store distribution of reams of paper has placed increasing demands on the wrapper due to rougher handling and more frequent re-stocking of the individual reams. Increased handling of the reams has resulted in more reams breaking open, damaging the wrapped paper product by allowing it to pick up moisture, tear, or get minor curl—physical damage that ultimately results in jams in the end-user's printer or copy machine. As a result, the market has demanded a stronger ream wrap.
At the same time, the market has demanded that manufacturers develop wrap materials with improved printing surfaces to enhance graphics and provide an eye-appealing wrapped product for the home office and small office consumer. One such material is a solid plastic film ream wrap that provides a smooth, high gloss surface for printing. Film ream wraps may also be transparent so that the paper product encased in the wrapper is visible from the outside of the package.
Traditionally, film ream wraps have consisted of one heavy weight film layer or two separate layers of solid, lighter weight plastic films laminated together with an adhesive. A primary disadvantage of current film ream wraps is the difficulty of handling slippery film materials on the manufacturers' packaging lines. Film wrappers tend to be slippery, causing the paper product to slip off-center while being wrapped on the packaging line. Manufacturers often must make costly modifications to traditional packaging lines in order to accommodate film ream wraps. Furthermore, film wrappers, which lack the structural strength and support of heavier weight paper laminates, coated papers, and paper/film wrappers, are more vulnerable to physical damage during shipping, handling, and storage. Another disadvantage of current film ream wraps is that, once the consumer opens the side seal of the wrapped package to remove sheets of paper, the wrapper can readily tear, exposing any paper remaining in the wrapper to physical damage, tearing, and moisture.
Thus, the market is demanding a stronger film ream wrap that provides an enhanced printing surface, greater structural support for the wrapper product, and less vulnerability to tearing and physical damage. The market also is demanding a film ream wrap that is easier to handle on traditional packaging lines, that facilitates the wrapping process by minimizing or preventing slippage of the paper product, and that obviates the need for costly modifications to traditional packaging operations. The present invention provides these added benefits.
U.S. Pat. Nos. 5,673,309 and 6,370,240 relate to a method of dispensing telephone cards from automatic teller machines and card constructions used therewith. Telephone time is appointed to a number of sheetlets printed with random numbers which serve as a personal identification number. They are packaged in bricks and activated when installed in an ATM or when dispensed.
Sheetlets, which are dispensed from the ATM machine, are currency sized and provide coefficient of friction on each surface thereof, and the coefficient friction differential enables dispensing of individual sheetlets of the group by caliper or opacity. Sheetlets have a lay flat quality. To assure proper single sheet dispensing, a telephone card sheetlet, must have the quality of being able to lay flat and having frictional characteristics to enable one sheetlet to be slid over another. The surfaces of the sheetlet should have a static coefficient of friction, namely the ratio of the force required to start moving a 193.3 gram sled across a surface divided by the weight of the sled, of about 0.55, preferably from about 0.45 to about 0.7. The coefficient of friction differential between one surface of the sheetlet to the other should be at least 25%, and within the range specified above. The coefficient of friction differential can be realized by coating the front and back surface of the sheetlet with a material which will, by its nature, inherently provide the coefficient of friction differential necessary to enable the sheetlets to be individually dispensed. Alternatively, the sheetlets can be supplied as a laminate of two different materials of different coefficients of friction to enable the sheetlets to be individually dispensed. One surface, may, for instance, be paper, and the other a polymer coating or self supporting polymer film such as polyester. This may be achieved by applying a polymeric coat from a solvent, emulsion, or as a hot melt to the surface of the paper.
U.S. Pat. No. 5,503,436 relates to an ATM dispensible self adhesive postage stamp construction. The postage stamp construction is formed of a plurality of postage stamps adhered to a currency sized release liner by an ooze resistant pressure sensitive adhesive which construction is coated with a polymeric coating on the face of the stamp and the under surface of the release liner and dispensible from an automatic teller machine.
The stamps comprise paper facestock and other paper weight of about 56 grams per meter squared having upper and lower surface. The upper surface is surfaced with stamped graphics and coated having a surface coefficient of friction greater than 0.45. The relevant frictional characteristics between slip over surfaces undercoating further prevent the dispensing of multiple stamp sheetlets.
Requirement for the overcoat and the undersurface whether coated or not is that the surface have a static coefficient of friction, namely, the ratio of the force required to start moving a 193.3 gram sled divided by the weight of the sled across about 0.45, preferably between 0.45 to about 0.7. This corresponds to 135 grams to a static face to imitate sled movement of about 87 grams to about 135 grams. It has been found that provided the friction requirements are met there should be at least a 25% difference between the coefficient of friction for the upper surface and the undersurface. This may be achieved by selection of paper or coatings as well as providing an irregular surface as by embossing or including in a coating filler or the like. The difference of the coefficient of friction will greatly aid in ensuring single sheetlet dispersing.
Friction is determined by securing a sheetlet to a flat surface placing a 193.3 gram sled measuring 6″×20.25″ on the sheetlet and pulling the sled with a force gauge to initiate movement of the sled over the sheetlet. The force measured is the force required to initiate movement of the sled over the sheetlet at a rate of 0.5 inch per minute.
For proper dispensing as measured by the static coefficient of friction of 0.45 to about 0.7, the coefficient of friction difference ensures preventing multiple dispensing of sheetlets from an automatic teller machine with coefficient of friction differential between the preferred upper and lower surfaces by about 25% or more.
U.S. Pat. No. 4,389,450 relates to a multiple layer packaging film in which the outer polymeric layers cooperate to achieve, between themselves, a relatively constant coefficient of friction differential, a thin seal capability, and a lap seal capability, even after the film is stored in round up rolled form.
In the making of multiple layer flexible plastic-type films, after the film is produced, it is wound up in roll form for storage or shipment. It is normal to use, as one of the outer layers of the film, a tacky heat sealable material, such as ethylene vinyl acetate. The other outer layer of the film, on its surface, may be a non-sealant layer composed of a non-tacky type polymer.
If the tacky material is used as the entire composition of the one outer layer, the tackiness may function as an adhesive in the roll, such that the tacky sealant layer sticks to the non-sealant layer.
To avoid the above problem of the tacky sealant layer sticking to the non-sealant layer, it has been normal practice to incorporate a slip additive into the tacky layer to reduce its tackiness. It is known that the slip additive gradually migrates to the outer surface of the tacky layer. When the film has been in roll form and is subsequently unrolled, testing reveals that the coefficient of friction (COF) of the sealant layer has increased since the roll was made, and the COF of the non-sealant layer has decreased.
These films are commonly used with packaging machinery which is sensitive to the COF of both surfaces of the packaging material. Desirably, the COF of the non-sealant layer is about 0.4 to 0.5, and the COF of the sealant layer is 0.2 to 0.3.
The invention provides a multiple layer, heat sealable, flexible packaging material, having a slip additive in the heat seal layer which material can be stored in roll form, and in which the coefficients of friction of the two surfaces of the film are substantially constant with time.
This invention is exemplified by a multiple layer heat sealable packaging sheet structure having, one of its surfaces, a sealant layer, and on the other surface, a non-sealant layer. The sealant and non-sealant layers are heat sealable each to themselves and to each other. The non-sealant has a coefficient of friction between about 0.4 and 2. The sealant layer has a coefficient of friction of less than about 0.3. Importantly, the coefficient of friction of both the sealant and non-sealant layers is substantially constant for a period of at least 30 days when the sheet structure is stored in the form of a continuous web wrapped about a central core, with the sealant and non-sealant layers in surface-to-surface contact.
In a preferred structure, the non-sealant layer is a blend which can best be comprehended as substantially a base polymer and a blended-in tacky additive. About 25% by weight to about 75% of the blend is the base polymeric material which, in unblended composition, has a coefficient of friction of less than about 2. About 75% by weight to about 25% of the blend is the additive polymeric material which, in unblended composition, has a coefficient of friction greater than 2.
The base polymeric material can be an ethylene copolymer such as ethylene vinyl alcohol. Other suitable polymers include polyester, polypropylene and nylon. The additive polymer is usually an ethylene copolymer and can consist of ethylene acrylic acid, ethylene methyl acrylate, ethylene ethyl acrylate, ethylene vinyl acetate and ionomer. It is important that the coefficient of friction of the normally tacky material used in the outside sealant layer be reduced, so that there is no tacky surface on the film which would stick to the packaging equipment. This is accomplished with slip additives which are known to reduce COF in this type of application.
The coefficient of friction used, is that obtained by ASTM D-1894, in which two surfaces of the one material are in friction surface-to-surface contact.
Polymer compositions having COF below 0.4 cannot be engaged by the packaging equipment without excessive slippage or excessive equipment wear. Polymer compositions having COF greater than about 2.0 have a tendency to stick to the equipment.
The entire film may be coextruded. Portions may be adhesive laminated, or extrusion laminated. In some cases, it is desirable that certain layers and particularly the non-sealant layer be oriented, either run axially, or biaxially. In a typical coextrusion process, the sealant layer composition is supplied to a first extruder. The non-sealant layer composition is supplied to a second extruder. The two compositions are extruded through the extruders and fed to a die where they are formed in a single, multiple layer film.